1. Field of the Invention
The present invention relates to an image capture device and, more particularly, to an apparatus and a method for compensating auto-focus of image capture device by utilizing red-eye eliminating function.
2. Description of Related Art
Generally, the auto-focus of an image capture device, such as a traditional camera or digital camera, is implemented as either an active focus or a passive focus device. The active focus device is widely employed in the point-and-shoot camera, which is similar to the traditional camera, but has an independent auto-focus device, such as a range finder consisting of an infrared transmitter and an infrared receiver, for measuring the distance between the camera and an object to be captured by detecting the brightness of the object. In contrast, the passive focus is widely employed in the medium/low level digital camera, which measures the distance between the camera and an object to be captured by analyzing a focal length evaluation value of the object obtained by a built-in image sensor.
However, for the active focus device, as mentioned above, an independent auto-focus device is required and the clearness of such an auto-focus device depends on the quality of the range finder. Furthermore, the cost is inevitably increased by incorporating such a range finder in the camera. As to the passive focus device, it is advantageous for saving cost by utilizing the built-in image sensor of the camera. Unfortunately, because the passive focus device relies on the focal length evaluation value, it presents a bad focus result when the object to be captured is in the dark state or the appearance of the object is too simple. FIG. 1 shows the graphs of focal length evaluation value versus focus position of lens for the dark and bright states. As shown, there is an obvious focal point in the bright state and thus the optimal focal length of the object can be easily determined. While in the dark state, there is no obvious focal point and the optimal focal length of the object is difficult to determine.
Therefore, it is desirable to provide a novel auto-focus apparatus and method to mitigate and/or obviate the aforementioned problems.
The object of the present invention is to provide an apparatus and a method for compensating auto-focus of image capture device by utilizing red-eye eliminating function, in which the low-cost passive auto-focus device is employed and the red-eye eliminating device, that is always activated before the flashlight is generated, is utilized as a light source to obtain a correct focus.
In one aspect of the present invention, an apparatus for compensating auto-focus of image capture device by utilizing red-eye eliminating function is provided. The apparatus comprises: an image sensor for capturing an image of an object so as to determine a focal length evaluation value of the object; a focal length adjuster for adjusting a focal length of the image capture device; a red-eye eliminating device capable of flashing for providing a red-eye eliminating function; and an auto-focus module for preliminarily determining a distance from the object to the image capture device based on the focal length evaluation value of the object captured by the image sensor to drive the focal length adjuster for performing a rough adjustment of the focal length of the image capture device, and when the red-eye eliminating device flashes for eliminating red-eye effect, further determining the distance from the object to the image capture device based on the focal length evaluation value of the object captured by the image sensor to drive the focal length adjuster, thereby performing a fine adjustment of the focal length of the image capture device.
In another aspect of the present invention, a method for compensating auto-focus of image capture device by utilizing red-eye eliminating function is provided. The method comprises the steps of: (A) using an image sensor to capture the image of an object so as to obtain a first focal length evaluation value, and using an auto-focus module to preliminarily determine a first distance from the object to the image capture device based on the first focal length evaluation value, thereby driving the focal length adjuster to perform a rough adjustment of the focal length of the image capture device; (B) driving a red-eye eliminating device to flash for at least one time to eliminate red-eye effect; and (C) whenever the red-eye eliminating device flashes to eliminate red-eye effect, using the image sensor to capture the image of the object so as to obtain a second focal length evaluation value of the object, and using the auto-focus module to determine a second distance from the object to the image fetching device based on the second focal length evaluation value of the object, thereby driving the focal length adjuster to perform a fine adjustment of the focal length of the image capture device.
Other objects, advantages, and novel features of the invention will become more apparent from the detailed description when taken in conjunction with the accompanying drawings.